Tracking Issue for extra UTF-16 methods

[clarfonthey]

Feature gate: #![feature(utf16_extra)]

This is a tracking issue for extra UTF-16 methods, which currently just includes u16::is_utf16_surrogate.

Public API

impl u16 {
    pub const fn is_utf16_surrogate(self) -> bool;
}

Steps / History

• Implementation of u16::is_utf16_surrogate (Add u16::is_utf16_surrogate #94713)
• Final comment period (FCP)
• Stabilization PR

Unresolved Questions

• What other useful UTF-16 methods should be exposed?

[bjoernager]

Could we also add the is_utf16_surrogate method to u32? I feel that it would be natural given the existing relationship between char and u32.

[clarfonthey]

What value do you see that method offering over just char::try_from?

[bjoernager]

There is the explicitness aspect to having a specifically-named function, but there is also the fact that <char as TryFrom<u32>>::try_from additionally trips on values greater than 0x10FFFF (and not just surrogates). It it also worth pointing out that TryFrom::try_from cannot be called from constant expressions.

[clarfonthey]

That's fair.

I'm mostly just thinking from the perspective of when it would be useful to know if a u32 is a UTF-16 surrogate value and not just when it's an invalid character, since I can't think of any.

[bjoernager]

It could be used for the sake of more verbose diagnostics in e.g. a conversion error, but I agree that the use cases may not be all that plentiful.